144 BROOM ALL : 



Equating T and C, 



32.2 Me h MV 



g g R 



32.2 e = h 



R 



hV^ 



(0 



32.2 R 



For all practical purposes we may assume h as equal to the 

 gauge, whence results 



e = 



(2) 



32.2 R 



which is the ordinary formula for the superelevation of the 

 rail. It will be noticed that e varies directly with the square 

 of the velocity and inversely as the radius of the curve. 

 Since the velocity of the trains varies, it is impossible to have 

 the superelevation correct under all circumstances. The best 

 to be done is to substitute for \' in formula (2) the average 

 speed of fast trains over the given curve. 



Returning now to the problem of passing from tangent to 

 curve on the above assumed simple track, it is seen that theo- 

 retically at the point of curve the superelevation must jump 



gV- 



instantaneouslv from e = o to e . This being 



32.2 R 



impossible, some method must be devised for passing in a 



more gradual manner through this critical point. 



There are two common methods in use for the solution of 

 the difficulty, one of them being only a more or less success- 

 ful makeshift, while the other method is l)oth theoretically 

 and practically a real solution of the problem. 



The first method consists in starting to superelevate the 

 track some distance in advance of the point of curve, so that 

 when the wheels reach the curve all or nearly all the superele- 



